A so-called “cooling/heating free type air conditioner,” which is an indoor-multi-type air conditioner including a plurality of indoor units and which is configured to be able to perform a cooling operation and a heating operation in parallel with each other, has been known (see, e.g., Patent Document 1). The air conditioner of Patent Document 1 includes a cooling/heating switching unit between an outdoor unit having an outdoor heat exchanger and indoor units each having an indoor heat exchanger. The outdoor unit is connected with the cooling/heating switching unit through two communication pipes. The cooling/heating switching unit is also connected with each of the indoor units through two other communication pipes.
In the air conditioner of Patent Document 1, the outdoor unit also includes a bridge circuit that defines the refrigerant flow directions to be constant in the communication pipes between the outdoor unit and the cooling/heating switching unit. On the other hand, changing the directions of the refrigerant flowing through the communication pipes between the cooling/heating switching unit and each indoor unit allows the indoor unit to selectively perform a cooling operation or a heating operation.
In the air conditioner of Patent Document 1, the communication pipes between the outdoor unit and the cooling/heating switching unit are comprised of a first communication pipe having a relatively small inside diameter and a second communication pipe having a larger inside diameter than the first one. During a cooling dominant operation in which a cooling load is heavier than a heating load, a high-pressure two-phase refrigerant or a high-pressure liquid refrigerant flows toward the indoor unit through the first communication pipe having the smaller inside diameter, whereas a low-pressure gas refrigerant flows toward the outdoor unit through the second communication pipe having the larger inside diameter. During a heating dominant operation where a heating load is heavier than a cooling load, a high-pressure gas refrigerant flows toward the indoor unit through the first communication pipe having the smaller inside diameter, whereas a low-pressure refrigerant flows toward the outdoor unit through the second communication pipe having the larger inside diameter.